Acrylic fibers having excellent pilling resistance and a process for producing the same

ABSTRACT

Acrylic fibers having excellent pilling resistance are disclosed. The acrylic fibers have a plurality of elongated wedge-shaped concave depressions extending into the fiber surface. And the acrylic fibers are produced by pre-treating acrylic fibers with a modifier to modify the outer layer of individual fiber and then after-treating the fibers with an organic solvent for acrylic fiber.

United States Patent [1 1 Orito et al.

[ Apr. 9, 1974 ACRYLIC FIBERS HAVING EXCELLENT PILLING RESISTANCE AND A PROCESS FOR PRODUCING THE SAME Inventors: Zen-Ichi Orito; Minoru Uchida;

Masatoshi Takesue; Hajime Sahara; Kihiro Fujii, all of Nagoya, Japan Mitsubishi Rayon (30., Ltd., Tokyo, Japan Filed: May 24, 1971 Appl. No.: 146,148

Assignee:

Foreign Application Priority Data May 27, 1970 Japan 45-45502 June 5, 1970 Japan..... 45-48614 June 8, 1970 Japan 45-49308 June 12, 1970 Japan 5-50834 US. Cl. 161/180, 53/] 14.6, 8/115.5,

57/140 R, 161/178 Int. Cl. D02g 3/00, D02g 3/22 Field of Search 161/180, 177, 178;

8/1 14.6, 115.5; 28/76 T; 57/140 R, 140 J [56] References Cited UNITED STATES PATENTS 2,862,284 12/1958 Wiczer 161/180 X 8/1960 Jankens 161/178 Primary Examiner-George F. Lesmes Assistant Examiner-Lorraine T. Kendell Attorney, Agent, or FirmArmstrong & Wegner [5 7] ABSTRACT Acrylic fibers having excellent pilling resistance are disclosed. The acrylic fibers have a plurality of elongated wedge-shaped concave depressions extending into the fiber surface. And the acrylic fibers are produced by pre-treating acrylic fibers with a modifier to modify the outer layer of individual fiber and then after-treating the fibers with an organic solvent for acrylic fiber.

3 Claims, 5 Drawing Figures PATENTEDAPR m 3802.954

FIG. 4A

The present invention relates to acrylic fibers having a plurality of elongated wedge shaped concave depressions extending into the fiber surface and process for producing the same n V V v H V 7 The term fibers herein used includes the staple fibers, spun yarns, tow, knitted fabrics and woven fab- I'ICS.

A. fibers have various excellent physical and chemical properties so that the fibers have been used in many fields including clothes. However, acrylic fibers have a defect that when the knitted or woven fabrics made of acrylic fibers are worn for long time or put under an action of rubbing such as washing, pills are formed on the surface of the fabrics. This phenomenon is well known as pilling and the pills spoil the beautiful appearance of the fabrics. Therefore, prevention of pilling has been earnestly desired.

Many attempts have been made to preventor eliminate the formation of pills on the surface of thefabrics.

For instance, such methods that particular conditions in fiber denier, fiber length and fiber cross section are used, or fibers are subjected to a finishing treatment with a resin have been used. However, satisfactory results have never been attained by such methods.

Further, in order to produce acrylic fibers having particular hand, the method has been used of making the fiber surface rough by embossing the fibers. However, the acrylic fibers obtained by this method has not been satisfied from the point of pilling resistance.

Accordingly, an object of the present invention is to provide acrylic fibers having excellent pilling resistance.

Another object of the present invention is to provide a process for producing acrylic fibers having excellent pilling resistance.

Further objects of the present invention will be clear from the descriptions that follows:

These objects of the present invention are achieved by pre-treating acrylic fibers with a modifier to make the outer layer of individual fiber insoluble in dimethyl formamide at 100C. and then after-treating the acrylic fibers with an organic treating agent whereby a plurality of elongated wedge shaped concave depressions extending into the fiber surface is formed.

According to the present invention, acrylic fibers having excellent pilling resistance as well as other excellent fiber properties can be produced without losing the preferable fiber properties of acrylic fiber.

FIGS. 1, 2 and'3 are scanning electron microscopic photographs showing the concave depressions formed into the surface of fibers. FIG. 4 is to illustrate the method of measuring depth of the depression.

As is shown in the scanning electron microphoto- The concave depressions shown in scanning electron microphotographs of FIGS. 1 and 2 are somewhat different from the definite rhombic concaves shown in the photograph of FIG. 3 and this is due to the difference in spinning conditions. Therefore, the elongated wedge shaped concaves into the surface of the fibers of the present invention include those having the shapes as shown in FIGS. 1 and 2 and those having the shape as shown in FIG. 3.

Acrylic fibers of the present invention have a plurality of elongated wedge shaped concave depressions described hereinbefore.

Number of the concave depressions is preferably from 5 to 50 per inch along the length of a individual fiberfAnd the concave depressions are preferably in rhombic shape, length (a) of the major-axis (elongated axis) of the individual depression is in the range of 0.5 p. to 20p. and the maximum depth (b) of the concave depressions is in the range of 0.2;1. to 10 1.. Major axis of the rhombic depressions is alligned in the direction of the fiber axis and the minor axis of the rhombic depres' sions is alligned in the direction perpendicular to the fiber axis.

The major axis and depth of the elongated wedge shaped concave depressions in the fibers of the present invention are measured with a scanning electron microscope [ISM Type II manufactured by Japan Electron Optics Laboratory Co., Ltd.]. Depth of the concave depressions is measured by taking photographs of the depression at two different angles in the same field of vision and calculating the depth in accordance with the following equation in reference to FIG. 4. FIG. 4(A) is a schematic view of the concave depression and FIG. 4(B) is an inclined schematic view of FIG. 4(A) at an angle of 6.

b p'lsin 0 p/tan 0 wherein b: Maximum depth of the elongated wedge shaped concave depression.

' p: Distance from the point 0 to the end point x of major axis.

p: Distance from the point 0 to the end point x of major axis after inclination by 0.

0: Angle of inclination of sample fiber.

For taking said two photographs, a sample inclining apparatus (Goniometer-specimen stage Type JSM-GS manufactured by Japan Electron Optics Laboratory Co., Ltd.) is used with an angle of inclination of 20.

The fibers of the present invention are produced, for example, by the following method. 7

In the present-invention, acrylic fibers are produced from acrylonitrile homopolymer, copolymer of acrylonitrile with at least one other monomer copolymerizable with acrylonitrile or their blend by the conventional spinning methods. The acrylonitrile copolymer preferably contains more than percent by weight of acrylonitrile and up to 20 percent by weight of at least one other monomer copolymerizable with acrylonitrile.

The other monomer includes vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, styrene, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, acrylamide, methacrylamide, methacrylonitrile, and monomers containing sulfoxyl group or their salts.

, methyl acetamide the pre-treatment is preferably carried out under such a condition thatmodified outer layer is 0.5 to 40 percent of the total cross sectional area of an individual fiber.

Then, thus pre-treated acrylic fibers are after-treated with at least one organic treating agent which is nonsolvent for the modified outer layer, but is solvent for the un-modified inner layer of the acrylic fibers. Method of said after-treatment with the organic treating agent is as follows: (A) The pretreated acrylic fibers are immersed in the organic treating liquid and then washed with water and dried, (B) the pre-treated acrylic fibers are immersed in an aqueous organic treating liquid, then squeezed and heat treated, or (C) the pre-treated acrylic fibers are treated with a vapor of the organic treating agent.

The pretreatment may be carried out on the acrylic fibers in a form of staple, tow, spun yarn, knitted or woven fabric.

' Acrylic fibers of the present invention may be mix spun with other kind of fibers. And when the present acrylic fibers are mix spun with fibers which are degraded with the modifier to be used, it is preferable that the'present acrylic fibers are pre-treated with the modifier, mix spun with other kind'of fibers and then after treated with the organic treating agent.

The cross-sectional area of the modified outer layer is measured as follows: that is, the sample of the pretreated fibers is embedded in monomeric n-butyl methac'rylate and heatedto cause polymerization. A specimen of the cross section of the fibers is prepared by the same means as in the preparation by optical microscope. Thereafter, the specimen is immersed in dimethyl formamide at 100C. .to dissolve unmodified inner layer of the fiber and the modified outer layer remained insoluble is photographed with a scanning electron microscope. The sectional area is calculated from the photograph.

The modifiers to be used for the pre-treatment iriclude, for example, saponifying agents such as alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium'hydroxide, and sulfuric acid and chemical reacting agents such as hydroxylamine sul-,

fate, and hydroxylarnine phosphate. v

The modification treatment is carried out so that area of the modified outer layer is 0.5.to 40 percent of cross sectional area of an individual acrylic fibers. However, actual conditions vary depending upon the kind of the modifiers, size of fibers, etc. Therefore, suitable modification treatment maybe carried out within the scope of the present invention. I f r Preferable. organic" treating agents for producing acrylicv fibers of the presentinvention areas follows:

i. Amide compounds dimethyl formamide, di-

ii.'Sulfon and 'sulfoxide compounds I oxide, dimethyl sulfon' iii. Carbonatecompounds ethylene carbonate iv. Nitrilecompounds malononitrile, adiponitrile,-

acetonitrile These organic treating agents may be used singly or jointly in the form of 100 percent solution or dilute solution. Furthermore, an inert viscosity increasing agent dimethyl surrsuch as ethylene glycol or glycerine may be added thereto.

Embodiments of the after-treating methods with these organic treating agents are as follows:

A In the method where fibers are immersed in the treating agent, the pre-treated acrylic fibers are immersed in a solution of the organic treating agent. The concentration of the solution is higher than 85 percent, treating temperature is 10 to 100C. and treating time is 2 minutes to 1 hour. In this embodiment, a mixture such as dimethyl formamide-ethylene carbonate, di-

methyl acetamide-ethylene carbonate may be used.

. B. In the method where fibers are immersed in the organic agent, squeezed and then heat treated, the pretreated fibers are immersed in an aqueous solution of the organic treating agent. Representative examples of the agents include dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide and ethylene carbonate. These organic treating agents may be preferably used in such a manner that amount of the agent adhered to the fibers immediately after squeezing is more than 15 percent, more preferably 15 percent to 100 percent of the'weight of the dried fiber. The heat treating temper ature is preferably 50C. to 120C. As to the concentration of the aqueous solution, heating temperature and heating time, there is no special limitation.

C. In the method where fibers are treated with a va- I pour of the organic agent, the pre-treated fibers are exposed in a vapour of organic solvents for acrylic fibers having a boiling point of lower than 250C. As the solvents for acrylic fibers, inorganic solvents may be used beside the organic solvents. However, the organic solvents such as dimethyl formamide, dimethyl acetamide and dimethyl sulfoxide are the most prefera bly used. When the pre-treated fibers are after-treated with inorganic solvents, the fibers themselves are swollen or dissolved to cause adhesion between the fibers. Furthermore, inorganic solvents are vapourized with difficulty. 7

It is difficult to give clear explanation of the mechanism of formation of the concave depressions extending into the fiber surface by treating the pre -treated acrylic fibers with the organic treating agent. However,

it is considered that the concave depressions are 7 formed due to extraction of the unmodified inner layer (soluble in dimethyl formamide) through the modified the present invention have an elongated wedge shape and the major axis of the depression is alligned lengthwise direction of the fiber axis and the minor axis of the depression is alligned in the direction perpendicular to the fiber axis. Said concave depressions are extending into the surface of the fibers and are dispersed in the whole surface of the fibers. Therefore, contact area between single fibers is decreased and thus the knitted or woven fabrics have soft hand and excellent shape stability.

The present invention ples.

will be illustrated by the Exam- EXAMPLE 1 115x15 ofarea ot' the outer layer to tliatof total sectional area of the fibers is also shown in Table B.

Then, thus treated yarns were immersed in l percent dimethylformamide at 25C for 20 minutes: to obtain the fibers having concave depressions shown in polymer cornprisi ng 9 3 percent by weight of acry-' lonitrile and 7 percent by weight of vinyl acetate was spun by the conventional wet spinning method to obtain a tow having monofilamentary denier of 3 and total Table B.

ram

Treating agent Concentra- Temperature Treating Area of outer Major axis (a) of Maximum depth (b) Number of depression/inch tion (C) time layer depression (a) of depression (1.1.)

(min).

Sodium 1.5 95 30 3 8 0.5 1.5 l8 hydroxide Potassium 3.0 95 30 I3 3 9 0.5 L5 hydroxide Sodium 1.5 95 30 l4 3 10 0.5 1.5 20 hydroxide Sulfuric acid 60.0 l5 18 L0 5 0.3 0.8 l7

pler to obtain slivers (high bulk fibers). A part of said 25 A copolymer of 93 percent by weight of 'acrylonitrile slivers were shrunk by a fiber setter to obtain regularfibers. Forty parts of the high bulk fibers and 60 parts of the regular fibers were worsted-spun to obtain high bulk two folded yarns (250/360 T/M) of 36 metric and 7 percent by weight of vinyl acetate was spun by i the conventional dry spinning method toobtain staple fibers(3 deniers per filament semi dull). The staple fibers were pre-treated with 2 percent aqueous solution counts. Said high bulk yarns were pre-treated with 0.5 f di h dr xid at 90C for 30 minutes, washed percent aqueous solution ofsodium hydroxide at 90C. for 30 minutes, then bleached with 1 percent aqueous solution of acetic acid at 98C. for 15 minutes, washed with water and dried. The fibers were insoluble in diwith water and dried. Y

A part of the pre-treated fibers-were embedded in monomeric n-butyl me'thacrylate and heated to effect polymerization. Thereafter, a specimen of cross section methyl formamide at 100C. Said insolubilized portion of the fibers having a thickness of about 5 p. was prewas 7 percent of total cross sectional area of the fiber.

Thus treated yarns were immersed at a liquid ratio of 1 50in the treating agents as shown in Table A to form pared. This specimen was immersed in dimethylformamide kept at 100C. to cause partial dissolution thereof. By this procedure, it was acknowledged that undissolved part was the outer layer of the fibers and the concave depressions having characteristics shown in 40 area of this Outer layer was 21 Percent Of total cross Table A.

As one example, microphotograph of the fibers treated with treating agent (1) in Table A by a scanning electron microscope is shown in FIG. 1.

sectional area. V

The pre-treated fibers were immersedin dimethyl- 'formamide at 25" C. for 5 minutes. .Then, solvent was removed by washing with water and dried. Elongated Treating agent Concentra- Tempera- Immersion Major axis (a) of Maximum depth (b) Number of depression/inch" tion ture (C) time (min.) depression (u) of depression (pt) g 1 98 25 -20 5-12 0.5 -2 40 Dimethylformamid I 2 /50 25 20 4 -io 0.5 2 r 25 Dimethylt'ormarnide/Ethylene carbonate (3) /10 2s 20 3-8 0.4-2 "id Y Ethylene carbonate water (4) i 98 2s 20 5-12- q 0.54 '40 Dimethylacetamide q *2 I (5) 98 so 20 z-s 0.5-2 1s Acetonitrile w W" M,

EXAMPLE 2 w i H V wwgaaasensaeav aepre aaamassrEr trea?"' The high bulk yarns produced by the same method as in Example 1 were pre-treated with aqueous solution of the modifiers shown in Table B to make the outer layer of the fibers insoluble in dimethyl-formamide at 100C.

65 were rhombic in shape, were intermittently formed extending into the surface of the fibers. The shapes of the concaves are shown in Table C. As referential Example, non-ptreated-fibers were immersed in dimethyl- I formamide at 25C. to cause dissolution of the fibers.

TABLE Fibers Major axis (a) of Depth (b) of Number of depression 01.) depression (u) depression/inch This Example 3 0.3 l 12 Referential 0 O 0 Example When the fiber-s ot this Example wi'eniki into knit- 1O 7 V V w I v A. 7 A i v7 7' C W W ted fabric, fabrics of excellent properties, especially in 5th grade No formation of pills and no change of surface i 4th grade A few pills and changes pillmg resistance and shape stability was obtained. 3rd grade Medium number of pins and changes A scanning electron microphotograph of the fibers 2nd grade Many pills and changes 1st grade Extremely many pills and changes obtained in this Example is shown in FIG. 3.

. EXAMPLE 4 l ligh bulk yarns in Example 1 were pre-treated with 2 percent aqueous solution of sodium hydroxide at 90C. for 30 minutes, and then bleached with 1 percent aqueous solution of acetic acid at 98C. for 15 minutes, washed with water and dried. The outer layer of the fibers was insoluble in dimethylformamide at 100C. and this insolubilized part was 21 percent of total cross sectional area of the fibers.

Thus pre-treated high bulk yarns were immersed in 30 percent aqueous solution of dimethylformamide kept at 25C. and then squeezed in such a manner that the amount of dimethylformamide solution adheredto the yarns was 70 percent of weight of dried fibers. Then. the yarns were heat treated for one hour in a drier kept at 90C. Said yarns were dyed and subjected to softening treatment and then were made into a sweater by 146 Full Fashion'knitting machine.

In the surface of the fibers, elongated wedge-shaped concave depressions were formed. The concave depressions have a length of major axis of 1.2 to 7 p. and a depth of 0.4 to 1 pi and number of depressions per 1 inch was 15.

'Aftertreat ing C oncentra- Major axis Maximum depth F urtherm'ore; the knitted fabric ample had soft hand and completely maintained excellent properties of acrylic fibers.

EXAMPLE 5 A copolymer of 94 percent by weight of acrylonitrile and 6 percent by weight of methyl acrylate was spun by the conventional dry spinning method to obtain staple fibers of 3 deniers per filament. The fibers werepretreated with 13 percent owf of hydroxylamine sulfate and 10 percent owf of sodium secondary phosphate at a liquor ratio of 1 10 at 98C.,for 30 minutes.

Sixty parts of thus pre-treated fibers (outer layer insoluble in dimethyl formamide at 100C. was 23 percent) and 40 parts of Merino woolwere mix spun to obtain 36 counts (metric count) two folded yarns. The yarns were immersed in aqueous solutions of the treating agents in Table E and were squeezed in such a manner that the amount of the-solution adhered to the 'fibers was 70 percent of weight of the dried fibers. Thereafter, the yarns were heat treated for 1 hour in a drier kept at 90C.

The states of the acrylic fibers in the yarns obtained are shown in Table E.

Number, of depression/inch type pilling tester and the results thereof are shown in 1 Table D. It is clear from the Table D that the knitted fabric. obtained in this Example had conspicuously excellent pilling resistance. 2

(Table D comparatively shows the ,test results on a knitted fabric obtained from conventional acrylic fi- Fabric I v Filling resistance (grade) I Fabric of this Example 7 5 Fabric of conventional acrylic fibers agent tion (3%) (a) of (b) of depression depression (1 "f Dimethyl-acetamide 30 1.5 so.s 1.0 20

Dimethyl-sulfoiiide 50 3.0 10. 0.8 3.0 45- Ethylene 50 3.0 10 0.8 3.0 40 v carbonate 7 1 V sa d knitted fabric was tested 'b y Ra ndom tumble EXAMPLE 6 f" Acrylic fibers (3 deniers per filament) were pretreated with 2 percent aqueous solution of sodium hydroxide at C. for 30 minutes and thenbleached with 2 percent aqueoussolution of oxalic acid at 98C. for 15' minutes. The outer layer of-the fibers thus pretreated was insoluble in dimethylformamide at 100C. and this outer layer was 21 percent of total cross sectional area of the fibers.

Said fibFsTeFE un into two folded ai'ns'i res/350" TIM) of 36 metric counts, which were exposed to saturated vapor of dimethylformamide at 100C. for 5 minutes, washed with water and dried. Thus treated yarns were dyed and subjected to softening-treatment and then made into knitted fabric. .In the fiber surface of this knitted fabric, elongated wedge-shaped concave depressions, having a major axis of 1.3 u. to 5 pi. and. a depth of 0.4 p. to 0.8 p. were formed. Number of the depressions was /inch.

Said knitted fabric had an excellent pilling resistance as shown in Table F.

Acrylic fiber two folded spun yarns (250/360 T/M) of 32 metric counts were immersed in a mixed aqueous solution of 10 percent of glycerine and 10 percent sulfuric acid, and then squeezed. Thereafter, the yarns were heated at 120C. for 10 minutes to pretreat the yarns, washed with water and dried. The outer layer of the fibers was insoluble in dimethylformamide at 100- C. and said outer layer of the fiber was percent of total sectional area of the fiber.

Thus pre-treated spun yarns were knitted into a fabric, which was treated in saturated vapor of the solvents What is claimed is:

1. Acrylic fibers each having an outer layer, and said fibers having a plurality of elongated wedge shaped concave depressions extending into the surface thereof, the number of said depressions being more than 3 per inch along the length of an individual fiber and the elongated axis of said depressions being axially aligned in the lengthwise direction of the fiber, wherein said outer layer of said fibers is insoluble in dimethyl formamide at 100C. and said outer layer is 0.5 to percent of the total cross sectional area of an individual fiber.

2. Acrylic fibers according to claim 1, wherein said concave depressions are rhombic in shape, length (a) of the elongated axis of the individual depression being in the range of 0.5 y. to 20 p. and the maximum depth (b) of said depressions being in the range of 0.2 u to 10 u, the major axis of said rhombic depressions being aligned in the direction of the fiber axis and the minor axis thereof being aligned in the direction perpendicular to the fiber axis.

3. Acrylic fibers according to claim 1, wherein said fibers contain at least 80 percent by weight of acrylonitrile and the number of said depressions ranges from 5 to 50 per inch along the length of an individual fiber.

25 shown in Table G for 5 minutes.

TABLE G After treating Vapor Length (a) of Maximum depth (b) of Number of depression/inch agent temperature major axis of depression (;1.)

(C) depression (1.1.)

Dimethyl-formamidc l.2 6 0.5 L5 19 Dimclhyl-sulfoxidc l.() 8 0.5 L5 20 Acelonitrile 80 l.4 l0 0.4 1.0 18 

2. Acrylic fibers according to claim 1, wherein said concave depressions are rhombic in shape, length (a) of the elongated axis of the individual depression being in the range of 0.5 Mu to 20 Mu and the maximum depth (b) of said depressions being in the range of 0.2 Mu to 10 Mu , the major axis of said rhombic depressions being aligned in the direction of the fiber axis and the minor axis thereof being aligned in the direction perpendicular to the fiber axis.
 3. Acrylic fibers according to claim 1, wherein said fibers contain at least 80 percent by weight of acrylonitrile and the number of said depressions ranges from 5 to 50 per inch along the length of an individual fiber. 